This invention relates in general to natural gas and in particular to natural gas fuel delivery systems.
Compressed natural gas (CNG) vehicles require specialized refueling delivery systems. U.S. Pat. No. 5,884,675 discloses one such system consisting of banks of cylinders each of which has an axially moveable piston, a pair of inlets, and an outlet. The cylinders are filled with CNG at a remote location and then transported to the refueling station. At the refueling station, hydraulic fluid is pumped from a reservoir into one end of each cylinder. The hydraulic fluid displaces the piston in each cylinder, forcing CNG through the outlet at the other end of the cylinder. The CNG flows through a hose into the vehicle being refueled. Each bank of cylinders is equipped with an accumulator located downstream from the outlets. When the cylinders are completely drained of CNG, the pressure in the accumulator moves each piston back to its starting position, forcing the hydraulic fluid out of the cylinders and back into the reservoir.
While this system represents an improvement over other CNG delivery systems, certain disadvantages remain. Each of the cylinders has a moveable piston and openings at each end, making them expensive to manufacture.
A compressed natural gas (CNG) refueling system has a hydraulic fluid reservoir containing hydraulic fluid, a pump, and reversible flow valves. The hydraulic fluid is of a type which does not readily mix with the CNG. The refueling system also includes cylinders containing CNG. Each cylinder has a fitting installed in an opening at one end. The fitting contains a hydraulic fluid port and a gas port. A tube extends within the cylinder from the hydraulic fluid port to a point adjacent to the opposite end of the cylinder. The opposite end of the cylinder is closed.
At the refueling station, hydraulic fluid is pumped from the reservoir through the hydraulic fluid port in each cylinder, displacing the CNG inside each cylinder and forcing the CNG out through the gas port of each cylinder. During fueling, hydraulic fluid is pumped from the reservoir to maintain 3600 psi of pressure in the cylinders. When a sensor detects that the cylinders are completely drained of CNG, the reversible flow valves will reverse orientation, allowing the hydraulic fluid to flow back into the reservoir. Once the cylinders are drained of hydraulic fluid, the cylinders may be disconnected and refilled with CNG.